Previous investigators (1,2,3,4, 5) have shown that a high serum cholesterol is commonly found in patients presenting the classical symptoms of myxedema. There has been a difference of opinion (6), however, as to whether high cholesterol invariably occurred and as to whether it was a sufficiently fundamental part of the syndrome to be of value in weeding out the atypical forms of hypothyroidism from the complex group of patients with low basal metabolic rates and such symptoms as retardation, weakness, easy fatigability, sensitivity to cold, falling hair, dry skin, obesity, etc. Certain authors, and particularly Hurxthal, have concluded that the level of cholesterol constitutes a valuable index of the degree of hypothyroidism, while others (7, 8, 9, 10) have found it unreliable and not an essential part of the syndrome. A contributing factor to this disagreement has been the difference in methods employed.The basal metabolic rate has not proved to be an infallible criterion of hypothyroidism. For example, it may be low without the syndrome of sensitivity to cold, edema, dry skin and coarse hair, or the patient may be so tense and excitable that relaxation essential to the measurement of the true basal metabolic rate is impossible.The present investigation was undertaken to study whether or not the levels of serum cholesterol, fatty acids, and phosphatides might furnish accurate criteria of thyroid deficiency and of the value of administering dessicated thyroid. A second purpose was to evaluate the effect of administering thyroid at the height of lipemia. Disorders in protein metabolism have been also described as occurring in myxedema, but the apparent changes in serum proteins may well have been compensatory responses to the disturbance in water metabolism. In order to obtain further insight into this problem, serum proteins and
